The present invention relates to a two-port vacuum valve connected between a vacuum chamber and a vacuum pump for reducing a pressure in the vacuum chamber, and more particularly, to a two-port vacuum valve having function for adjusting a valve-opening.
In producing procedure of semiconductors, when a pressure in a vacuum chamber is reduced using a vacuum pump, a two-port vacuum valve is connected in a flow passage connecting a vacuum chamber and a vacuum pump, and a flow passage is opened and closed by the vacuum valve. In the vacuum valve used in such a manner, generally, a valve member which opens and closes the flow passage is driven by a piston, and a stroke of the piston corresponds to an opening of the valve member.
Depending upon various using conditions such as capacity of the vacuum chamber and pressure-reducing ability of the vacuum pump, the opening of the vacuum valve is not changed in accordance with the using conditions or the flow passage is not fully opened at a dash, and in many cases, it is required to divide the changing operation of the opening operation into a plurality of steps in such a manner that the flow passage is once opened in a limiting manner to carry out initial pressure reduction and then the flow passage is fully opened.
According to the conventional vacuum valve, however, since the stroke of the piston directly corresponds to the valve-opening as the above mention and the opening can not be adjusted, the above requirement can not be satisfied.
It is an object of the present invention to provide a two-port vacuum valve capable of adjusting valve-opening depending upon the using conditions and the like and having excellent function.
To achieve the above object, the present invention provides a two-port vacuum capable of adjusting the valve-opening comprising a valve housing having a first main port, a second main port to be connected to a vacuum chamber and a vacuum pump and a main flow passage which connects both the main ports with each other, a main valve member provided in the valve housing for opening and closing the main flow passage, a cylinder connected to the valve housing, a first piston and a second piston accommodated in a piston chamber of the cylinder such that these pistons can independently slide and abut against each other, a first pressure chamber formed between the first piston and a first end wall on the side of one end of the cylinder, and a second pressure chamber formed between the second piston and a second end wall on the side of the other end of the cylinder, a first operation port and a second operation port for respectively supplying pressure fluid to the first pressure chamber and the second pressure chamber, a first rod slidably passing through a first end wall of the cylinder and connecting the first piston and the main valve member with each other, a second rod slidably passing through a second end wall of the cylinder and having one end connected to the second piston and the other end extending outside of the cylinder, a positioning mechanism which comprises a stopper mounted to the second rod such that its position can be adjusted and an abutting portion against which the stopper abuts and stops, and which defines a forward movement position of the second piston, and a return spring for biasing the main valve member in its closing direction.
In the vacuum valve of the present invention having the above structure, if pressure fluid is supplied from the second operation port to the second pressure chamber, the second piston moves forward toward the first piston, the stopper stops at an intermediate position where the stopper abuts against the abutting portion. If pressure fluid is supplied from the first operation port to the first pressure chamber while keeping the pressurizing state of the second operation port, the first piston that has moves forward by the return spring retreats toward the second piston. Therefore, the main valve member opens, and the first piston opens the main flow passage by a stroke which is limited until the first piston abuts against the second piston. The valve-opening at that time can freely be adjusted by changing the position of the stopper along the second rod.
When the main valve member is to be further opened fully from the above state, if the second operation port is evacuated while keeping the pressurizing state of the first operation port, the first piston and the second piston retreat together, and the main valve member is fully opened.
According to the vacuum valve of the present invention, it is possible to adjust the valve-opening of the main valve member and to open the main valve member in two stages with simple means to define the stroke of the first piston which drive the main valve member by the second piston.
In the present invention, the piston chamber of the cylinder has uniform inner diameter entirely, the first piston and the second piston have the same diameters.
Further, it is preferable that surfaces of the first piston and the second piston which abut against each other are formed with projections and recesses which are fitted to each other at the time of abutment.
In the present invention, the vacuum valve may comprise an auxiliary valve mechanism which opens and closes the main flow passage in a limited manner. The auxiliary valve mechanism comprises an auxiliary flow passage formed such as to establish a short circuit in the main flow passage, an auxiliary valve member for opening and closing the auxiliary flow passage, an auxiliary piston slidably accommodated in the first piston, an auxiliary rod which is movably inserted into the first rod and which connects the auxiliary valve member and the auxiliary piston with each other, an auxiliary pressure chamber for applying fluid pressure to the auxiliary piston in a valve-opening direction, an auxiliary operation port for supplying pressure fluid to the auxiliary pressure chamber, and a return spring for biasing the auxiliary valve member in a valve-closing direction.
It is preferable that the auxiliary valve mechanism includes an adjusting shaft which adjust a valve-opening of the auxiliary valve member, the adjusting shaft slidably passes through the second rod and second piston and is thread-typed connected to the first piston, a tip end of the adjusting shaft abuts against a back surface of an auxiliary piston in the first piston, a stroke of the auxiliary piston can be adjusted by adjusting a connection position between the first piston and the adjusting shaft.